Study of gate induced sensitivity amplification in carbon nanotube thin film transistor based ammonia sensor

Abstract

Gas sensors based on carbon nanotube thin film transistors (CNT TFT) have been widely investigated in the past. However, studies on the active sensing properties i.e. effects of gate induced variations in sensing of such devices are deficient. In this work the effects of gate voltage on the ammonia sensing properties of a single wall CNT TFT are investigated. It is observed that under the influence of a gate field, the device sensitivity and detection limit (LOD) can be improved by more than 11 and 6 times respectively. The amplification of sensor response is found to occur for both the gate polarities and this is attributed to a combination of two phenomena. Firstly, ab-initio Molecular dynamics (MD) based adsorption studies of ammonia molecules to a CNT device indicate that the introduction of a gate field leads to an increase in the adsorption energy of ammonia to the device especially for a positive gate which is directly relatable to the observed amplification in sensing. Additionally, in the negative gate regime, a reversible increase of the contact resistance induced by ammonia exposure is thought to be the primary contributing factor in increasing the responsivity of the sensor. This is also thought to contribute to improving the sensor selectivity at negative gate.